Flooring systems currently used in housing, commercial and light industry buildings are of light timber framing, concrete or combined concrete and structural steel. Light timber framing has serious disadvantages in respect to its combustible content, its high labor and material costs and its span limitations. The use of the open web timber joist attempts to overcome the span limitations but does so with considerable increase of overall floor thickness. Reinforced concrete floor systems have high load carrying capacity, are non-combustible but become excessively heavy in long span applications. In addition the cost of forming is excessive when limited repetition is involved. Precast concrete elements are useful for longer spans but require engineering and crane services to construct. Systems utilizing open web steel joists with a light metal deck to serve as the underside form for a cast in place floor slab are ideal for longer spans but are not economical for relatively short and intermediate spans. Housing contractors are often reluctant to utilize structural steel. The overall thickness of open web steel joist floor is also considerable.
Light timber framing is undesirable because of its combustibility and span limitation; total concrete systems have some advantages but some serious disadvantages. Existing combined concrete and steel systems similarly have some advantages and some disadvantages.